Normalize property names from OAS into valid Terraform attribute name

Background

Currently, when an OAS is mapped to provider code specification, we use the property names directly from the JSON schema properties as the attribute name. Example:

OAS

"Pet": {
    "required": [
        "photoUrls"
    ],
    "type": "object",
    "properties": {
        // .. other properties
        "photoUrls": {
            "type": "array",
            "items": {
                "type": "string"
            }
        }
    }
},

Provider Code Spec

{
    "name": "pet",
    "schema": {
        "attributes": [
            // .. other properties
            {
                "name": "photoUrls",
                "list": {
                    "computed_optional_required": "required",
                    "element_type": {
                        "string": {}
                    }
                }
            }
         ]
    }
}

Here, photoUrls is not a valid Terraform attribute identifier and must match the regex ^[a-z_][a-z0-9_]*$:

Must start with a lowercase letter or underscore
Only lowercase letters, numbers, or underscores allowed

Solution

It seems unrealistic to expect an OpenAPI spec to account for Terraform attribute naming, so we should attempt to normalize property names before serializing. This could prove tricky as the configuration has some options that reference OAS attributes, such as schema -> attributes -> aliases and schema -> attributes -> overrides.

As for how/what to normalize, we'll need to make pragmatic decisions on how far to go with the normalization, but an initial proposal:

camelCase -> camel_case
PascalCase -> pascal_case
UPPERCASE -> uppercase
snake_case -> snake_case

We should also consider how to handle special characters that can't be normalized, like <extra_key>, and whether we want to remove those characters -> extra_key

We will also run into the problem of potential conflicts when normalizing a property name:

"Pet": {
    "required": [
        "photoUrls"
    ],
    "type": "object",
    "properties": {
        // .. other properties
        "photo_urls": {
            "type": "array",
            "items": {
                "type": "string"
            }
        },
        // this would be normalized to photo_urls, conflict!
        "photoUrls": {
            "type": "array",
            "items": {
                "type": "string"
            }
        }
    }
},

hashicorp / terraform-plugin-codegen-openapi